This invention was made with the support of the Government of the United States of America, and the Government of the United States of America has certain rights in the invention.
The present invention relates to materials and methods of activating T-cells with specificity for particular antigenic peptides, the use of activated T-cells in vivo for the treatment of a variety of disease conditions, and compositions appropriate for these uses.
The efficiency with which the immune system cures or protects individuals from infectious disease has always been intriguing to scientists, as it has been believed that it might be possible to activate the immune system to combat other types of diseases. Such diseases include cancer, AIDS, hepatitis and infectious disease in immunosuppressed patients. While various procedures involving the use of antibodies have been applied in those types of diseases, few if any successful attempts using cytotoxic T-cells have been recorded.
Theoretically, cytotoxic T-cells would be the preferable means of treating the types of disease noted above. However, no procedures have been available to specifically activate cytotoxic T-cells.
Cytotoxic T-cells, or CD8 cells as they are presently known, represent the main line of defense against viral infections. CD8 lymphocytes specifically recognize and kill cells which are infected by a virus. Thus, the cost of eliminating a viral infection is the accompanying loss of the infected cells. The T-cell receptors on the surface of CD8 cells cannot recognize foreign antigens directly. In contrast to antibodies, antigen must first be presented to the receptors.
The presentation of antigen to CD8 T-cells is accomplished by major histocompatibility complex (MHC) molecules of the Class I type. The major histocompatibility complex (MHC) refers to a large genetic locus encoding an extensive family of glycoproteins which play an important role in the immune response. The MHC genes, which are also referred to as the HLA (human leucocyte antigen) complex, are located on chromosome 6 in humans. The molecules encoded by MHC genes are present on cell surfaces and are largely responsible for recognition of tissue transplants as xe2x80x9cnon-selfxe2x80x9d. Thus, membrane-bound MHC molecules are intimately involved in recognition of antigens by T-cells.
MHC products are grouped into three major classes, referred to as I, II, and III. T-cells that serve mainly as helper cells express CD4 and primarily interact with Class II molecules, whereas CD8-expressing cells, which mostly represent cytotoxic effector cells, interact with Class I molecules.
Class I molecules are membrane glycoproteins with the ability to bind peptides derived primarily from intracellular degradation of endogenous proteins. Complexes of MHC molecules with peptides derived from viral, bacterial and other foreign proteins comprise the ligand that triggers the antigen responsiveness of T-cells. In contrast, complexes of MHC molecules with peptides derived from normal cellular products play a role in xe2x80x9cteachingxe2x80x9d the T-cells to tolerate self-peptides, in the thymus. Class I molecules do not present entire, intact antigens; rather, they present peptide fragments thereof, xe2x80x9cloadedxe2x80x9d onto their xe2x80x9cpeptide binding groovexe2x80x9d.
For many years, immunologists have hoped to raise specific cytotoxic cells targeting viruses, retroviruses and cancer cells. While targeting against viral diseases in general may be accomplished in vivo by vaccination with live or attenuated vaccines, no similar success has been achieved with retroviruses or with cancer cells. Moreover, the vaccine approach has not had the desired efficacy in immunosuppressed patients. At least one researcher has taken the rather non-specific approach of xe2x80x9cboostingxe2x80x9d existing CD8 cells by incubating them in vitro with IL-2, a growth factor for T-cells. However, this protocol (known as LAK cell therapy) will only allow the expansion of those CD8 cells which are already activated. As the immune system is always active for one reason or another, most of the IL-2 stimulated cells will be irrelevant for the purpose of combatting the disease. In fact, it has not been documented that this type of therapy activates any cells with the desired specificity. Thus, the benefits of LAK cell therapy are controversial at best, and the side effects are typically so severe that many studies have been discontinued.
Several novel molecules which appear to be involved in the peptide loading process have recently been identified. It has also been noted that Class I molecules without bound peptide (i.e., xe2x80x9cemptyxe2x80x9d molecules) can be produced under certain restrictive circumstances. These xe2x80x9cemptyxe2x80x9d molecules are often unable to reach the cell surface, however, as Class I molecules without bound peptide are very thermolabile. Thus, the xe2x80x9cemptyxe2x80x9d Class I molecules disassemble during their transport from the interior of the cell to the cell surface.
The presentation of Class I MHC molecules bound to peptide alone has generally ineffective in activating CD8 cells. In nature, the CD8 cells are activated by antigen-presenting cells which present not only a peptide-bound Class I MHC molecule, but also a costimulatory molecule. Such costimulatory molecules include B7 which is now recognized to be two subgroups designated as B7.1 and B7.2. It has also been found that cell adhesion molecules such as integrins assist in this process.
When the CD8 T-cell interacts with an antigen-presenting cell having the peptide bound by a Class I MHC and costimulatory molecule, the CD8 T-cell is activated to proliferate and becomes an armed effector T-cell. See, generally, Janeway and Travers, Immunobiology, published by Current Biology Limited, London (1994), incorporated by reference.
Accordingly, what is needed is a means to activate T-cells so that they proliferate and become cytotoxic. It would be useful if the activation could be done in vitro and the activated cytotoxic T-cells reintroduced into the patient. It would also be desirable if the activation could be done by a synthetic antigen-presenting matrix comprised of a material such as cells which not only presents the selected peptide, but also presents other costimulatory factors which increase the effectiveness of the activation.
It would also be advantageous if it was possible to select the peptide so that substantially only those CD8 cells cytotoxic to cells presenting that peptide would be activated.
The present invention relates to a synthetic antigen-presenting system for presenting an MHC molecule complexed to a peptide and an assisting molecule to a T-cell to activate the T-cell.
In one embodiment, the system relates to a synthetic antigen-presenting matrix having a support and at least the extracellular portion of a Class I MHC molecule capable of binding to a selected peptide operably linked to the support. The matrix also includes at least an extracellular portion of an assisting molecule operably linked to the support. The two extracellular portions are present in sufficient numbers to activate a population of T-cell lymphocytes against the peptide when the peptide is bound to the extracellular portion of the MHC molecule.
It has been found that an antigen-presenting matrix having both an MHC molecule or a portion of a MHC molecule together with an assisting molecule, or at least an extracellular portion of an assisting molecule, provides a synergistic reaction in activating T-cell lymphocytes against the peptide. Examples of assisting molecules are costimulatory molecules such as B7.1 and B7.2 or adhesion molecules such as ICAM-1 and LFA-3. It has been found that a specifically effective synergistic reaction results from an antigen-presenting matrix having MHC molecules bound with a peptide, a costimulatory molecule, and an adhesion molecule.
The support used for the matrix can take several different forms. Examples for the support include solid support such as metals or plastics, porous materials such as resin or modified cellulose columns, microbeads, microtiter plates, red blood cells and liposomes.
Another type of support is a cell fragment, such as a cell membrane fragment or an entire cell. In this embodiment, the matrix is actually cells which have been transfected to present MHC molecules and assisting molecules on the cell surface. This is done by producing a cell line containing at least one expressible Class I MHC nucleotide sequence for the MHC heavy chain, preferably a cDNA sequence, operably linked to a first promoter and an expressible xcex2-2 microglobulin nucleotide sequence operably linked to a second promoter. The MHC heavy chain and the xcex2-2 microglobulin associate together form the MHC molecule which binds to the peptide. The MHC protein binds with the antigenic peptide and presents it on the surface of the cell. The cell also includes a gene for a nucleotide sequence of an assisting molecule operably linked to a third promoter. The assisting molecule is also presented on the surface of the cell. These molecules are presented on the surface of the cell in sufficient numbers to activate a population of T-cell lymphocytes against the peptide when the peptide is bound to the complexes.
The cell line is synthetic in that at least one of the genes described above is not naturally present in the cells from which the cell line is derived. It is preferable to use a poikilotherm cell line because MHC molecules are thermolabile. A range of species are useful for this purpose. See, for example, U.S. Pat. No. 5,314,813 to Petersen et al. which discusses numerous species for this use and is incorporated by reference. It is preferred to use eukaryotic cells and insect cells in particular.
In one embodiment, it is particularly preferred to have at least two assisting molecules, one being a costimulatory molecule and the other being an adhesion molecule. It has been found that this combination has a synergistic effect, giving even greater T-cell activation than either of the individual molecules combined. It has also been found to be advantageous and preferable to have at least one of the transfected genes under control of an inducible promoter.
Using the present invention, it is possible to introduce the peptide to the cell while it is producing MHC molecules and allow the peptide to bind the MHC molecules while they are still within the cell. Alternatively, the MHC molecules can be expressed as empty molecules on the cell surface and the peptide introduced to the cells after the molecules are expressed on the cell surface. In this latter procedure, the use of poikilotherm cells is particularly advantageous because empty MHC molecules, those not yet complexed or bound with peptides, are thermolabile.
Class I MHC molecules have been expressed in insect cells such as Drosophila melanogaster (fruit fly) cells. Since Drosophila does not have all the components of a mammalian immune system, the various proteins involved in the peptide loading machinery should be absent from such cells. The lack of peptide loading machinery allows the Class I molecules to be expressed as empty molecules at the cell surface.
Another advantage of using insect cells such as the Drosophila system is that Drosophila cells prefer a temperature of 28xc2x0 C. rather than 37xc2x0 C. This fact is very important, because empty Class I molecules are thermolabile and tend to disintegrate at 37xc2x0 C. By incubating the Class I-expressing Drosophila cells with peptides that can bind to the Class I molecule, it is possible to get virtually every Class I molecule to contain one and the same peptide. The cells are accordingly very different from mammalian cells, where the Class I molecules contain many different types of peptides, most of which are derived from our own, innocuous cellular proteins.
The present invention also relates to methods for producing activated CD8 cells in vitro. One method comprises contacting, in vitro, CD8 cells with one of the antigen-presenting matrices described above for a time period sufficient to activate, in an antigen-specific manner, the CD8 cells. The method may further comprise (1) separating the activated CD8 cells from the antigen-presenting matrix; (2) suspending the activated CD8 cells in an acceptable carrier or excipient; and (3) administering the suspension to an individual in need of treatment. The antigens may comprise native or undegraded proteins or polypeptides, or they may comprise antigenic polypeptides which have been cleaved into peptide fragments comprising at least 8 amino acid residues prior to incubation with the human Class I MHC molecules.
In another variation, the invention relates to methods treating conditions in patients and specifically killing target cells in a human patient. The method comprises (1) obtaining a fluid sample containing resting or naive CD8 cells from the patient; (2) contacting, in vitro, the CD8 cells with an antigen-presenting matrix for a time period sufficient to activate, in an antigen-specific manner, the CD8 cells; and (3) administering the activated CD8 cells to the patient. The invention also relates to the method of treating a medical condition by administration of an antigen-presenting matrix in a suitable suspension. In various embodiments the condition may comprise cancer, tumors, neoplasia, viral or retroviral infection, autoimmune or autoimmune-type conditions. In one embodiment, the method of administering the matrix comprises intravenous injection.